In the etching step of the semiconductor device fabrication process, treatment is carried out in a corrosive halogen-base gas plasma atmosphere. While the etching system includes parts which are exposed to the halogen-base gas plasma, parts having coatings formed by spraying yttrium oxide or yttrium fluoride to the surface of metallic aluminum or aluminum oxide ceramic substrates are known to be fully corrosion resistant and used in practice. See Patent Documents 1 to 4. Typical corrosive halogen-base gases used in the process for manufacturing semiconductor devices are fluorine-base gases such as SF6, CF4, Cl3, ClF3 and HF and chlorine-base gases such as Cl2, BCl3 and HCl.
Yttrium oxide-deposited parts obtained by atmospheric plasma spraying of yttrium oxide suffer from few technical problems and have long been utilized as semiconductor-related spray members. On the other hand, yttrium fluoride-sprayed coatings suffer from technical problems despite excellent corrosion resistance. For example, during atmospheric plasma spraying of yttrium fluoride, the yttrium fluoride is passed through a flame of 3,000° C. or higher and melted therein, whereby the fluoride can be decomposed. Then the coating partially contains a mixture of fluoride and oxide. For this reason, the practical utilization of yttrium fluoride-deposited parts is delayed as compared with the oxide-deposited parts.
When yttrium oxide-deposited parts are used in the etching process with fluorine gas, there arises the problem that the etching process becomes unstable because outermost yttrium oxide reacts with a fluorine-base gas at the initial of the process, and so the fluorine-base gas concentration within the equipment varies. This problem is known as “process shift.” The replacement by yttrium fluoride-deposited parts is under consideration. However, yttrium fluoride tends to have slightly low corrosion resistance in a halogen-base gas plasma atmosphere, as compared with yttrium oxide. In addition, yttrium fluoride sprayed coatings have many crevices on their surface and release many particles, as compared with yttrium oxide sprayed coatings.
It is thus believed that yttrium oxyfluoride having characteristics of both yttrium oxide and yttrium fluoride is more advantageous. Patent Document 5 discloses such an attempt. While yttrium oxyfluoride-deposited parts are prepared by standard atmospheric plasma spraying of yttrium oxyfluoride, the deposition of yttrium oxyfluoride sprayed coatings is difficult because a compositional shift of fluorine depletion and oxygen enrichment occurs due to oxidation.